The invention relates to non-glossy pigments having improved properties.
Traditional absorption pigments, such as, for example titanium oxide or iron oxide usually consist of very small parties having a size of typically 0.1-1 .mu.m, which absorb and/or strongly scatter specific wavelengths or wavelength regions of the incident light, the color effect being due to the remaining components of the incident light.
Such pigments have high hiding power, and their optical properties can be influenced by the average particle size. In general, as the average particle size decreases, an increase in color purity and color strength is observed.
However, these advantages with respect to their optical properties are accompanied by several serious disadvantages in terms of practical application. In general, pigments of very fine particle size exhibit unsatisfactory dispersibility which deteriorates further with decreasing particle size. This may be due to the strong tendency of very fine particles to form agglomerates, which can only be eliminated with large expenditures of energy and time and with the use of special dispersing apparatuses.
This tendency to form agglomerates reduces the color quality in a pigment formulation and simultaneously increases the amount of pigment required for achieving a specific color saturation in the pigment formulation, again adversely affecting the viscosity of the formulation.
Accordingly, the application of traditional nonglossy pigments is governed by the following rule of thumb: the higher the optical quality of these pigments, the more difficult and more expensive the processability (see G. D. Parfitt, Dispersion of powders in liquids, Elsevier Science Publishing Co., New York 1986).
In addition, traditional absorption pigments show high oil absorption in formulations and are distinguished by poor skin feeling.
Unlike traditional non-glossy pigments, pearl luster pigments are based on platelet-shaped substrates, in particular those made of mica, which are covered with one or more layers of one or more metal oxides, these platelet-shaped substrates having average diameters of typically 15-200 .mu.m. Owing to the smooth surfaces and the higher average particle diameter, these pigments have a substantially improved processability in formulations. The optical properties are characterized by high gloss and low biding power, which may be due to the transparent or semi-transparent substrate material.
Pigments combining the properties of traditional pigments (high color purity, no gloss) with good processability of pigments having larger particle sizes have already been proposed in the literature. Thus, for example, EP 0 406 657 proposes to deposit individual pigment particles in the submicron region instead of uniform, compact metal oxide coatings on mica substrates. The pigments thus obtained, which are also designated as transparent colors, do not exhibit any gloss, unlike pearl luster pigments, due to increased light scattering on the submicron pigment particles, but are characterized, like the latter, by low hiding power.
Accordingly, there was a great need for non-glossy pigments which are distinguished by advantageous optical properties and, in particular, high color intensity and high hiding power and by good processability and good skin feeling.